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The results in this paper demonstrate that Ishikawa endometrial monolayer cells become multinucleated by a process of nuclear “donation” from neighboring cells. As the resulting polyploid cell detaches from the colony in which it was formed, it is possible to detect mitonucleon(s) in the center of the cell. The mitonucleon is a transient mitochondrial superstructure surrounding aggregated chromatin (Fleming et al. 1998) with characteristics of the family of mitochondrial superstructures that are sometimes called spheroids or cup-shaped mitochondria (Fleming, 2016a). As was recently demonstrated gas vacuoles form within mitonucleons (Fleming, 2018). In the free-floating single cell, the retained gas creates a central vacuole, and the cell becomes a spheroid that floats above the monolayer. It resembles a “signet ring cell” in being characterized by a central vacuole and chromatin compressed against the vacuole membrane. The resulting structure is a spheroids that is hollow and unicellular, albeit polyploid. But whereas signet ring cells are assumed to be undergoing apoptosis, that is not the case for unicellular spheroids. Complete spheres with chromatin and cytosolic cell contents compressed against the cell membrane can be found floating independently above Ishikawa monolayers. When an isolated sphere settles back onto the surface of the petri dish, it is possible to observe dissipating gas bubbles within the now flattened sphere for a short period of time. When the gas is discharged the resulting cell looks like a typical giant polyploid cell.
Many researchers have presented data on the fascinating interactions of nuclei and mitochondria. With an interest in cell differentiation, I developed a protocol that resulting in the differentiation of Ishikawa endometrial cells first into domes, fluid-filled hemicysts, and then into gland-like structures. As I studied this process, I discovered a remarkable interaction between mitochondria and the nuclear aggregates formed in syncytia within hours of the addition of the inducing serum factor. Studying the approximately 24 hour differentiation process, it became clear that structures called mitonucleons develop as aggregated chromatin becomes surrounded by mitochondria fusing into spheroids or cup-shaped structures. As a result of the structure, small vacuoles formed in aggregated chromatin and a large vacuole formed within the mitonucleon in a separate compartment from the chromatin. The vacuoles in chromatin result in cells with "optically clear nuclei" a phenomenon observed in both normal and cancerous cells. The large vacuole in the mitonucleon resembles the central vacuole characterizing cells that are called "signet ring" cells and are also frequently found in cancerous tissue. In this paper, we look at another example of mitonucleon formation, this time in single cells within colonies of Ishikawa cells growing in monolayers. Initially the cells become multinucleated, mitonucleons form as the resulting polyploid cell detaches, gas accumulates within the mitonucleon and the entire cell becomes a floating spheroid with nuclei and cell contents pushed to the extreme edges of the spheroid by the pressure exerted by accumulating gases. When conditions are right, this unicellular spheroid can reattach to the dish, discharging the accumulated gas, becoming a cell with giant nuclei that can give rise to smaller nuclei, thereby initiating the development of a new colony.